Liquid Crystals

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Liquid Crystals

• Danielle Williams
• Dept of Physics
• University of Texas at Arlington

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Introduction

• Liquid crystals are very important in the study
  of optics, chemistry and polymer science. The
  discovery of the liquid crystal happened over a
  century and since this time the phenomena has
  been applied to many products in our society.
  This presentation will cover the properties,
  different phases and uses of liquid crystals. It
  will also give illustrations of liquid crystals
  from the micro perspective.

3
What are liquid crystals ? Liquid crystals form
from organic compounds and is thought of as the
phase of matter between the solid and liquid
state of a crystal.This phenomena was discovered
in 1888 by Austrian chemist Frederich Reinitzer.
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Phases
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Nematic Phase

• Molecules in this phase are long and rod-like in
  shape. They are free to move in space.

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Chiral Nematic

• This phase is composed of nematic molecules in a
  helical structure about the layer normal.
• The distance that it takes for the molecules to
  complete one turn is called the pitch.

? npcos?
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Smectic Phase

• This phase can be reached at lower temperatures
  than the nematic phase.
• Molecules align themselves in layers.(They are
  restricted to their plane.)
• More order and higher viscosity

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Columnar Phase

• Characterized by its stacked columns of
  molecules.
• Discovered in 1977 by Chandrasekhar

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Order Parameter

• S ½lt(3cos²?-1)gt
• The order parameter in a liquid crystal range
  from 0.3 to 0.9

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Electric field Effects

• If an electric field is applied to a liquid
  crystal the molecules will align in the same
  direction as the field.

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Twisted Nematic

• This is called the twisted nematic liquid crystal
  and the spacing between the planes change with
  temperature. The spacing is associated with the
  wavelengths of light.

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Applications
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Uses of Liquid Crystals

• Flat screen television
• Wristwatches
• Laptop screens
• Digital clocks
• Thermometers
• Switchable windows

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Conclusion

• We know today that many chemical compounds can
  exist in the liquid crystal state, such as
  cholesteryl benzoate. Thanks to the scientists
  that worked so diligently toward understanding
  this phenomenon, the world can focus on ways to
  make this product useful in society. Over the
  last century many applications such as the
  detection of hot points in microcircuits, the
  findings of fractures or tumors in humans and the
  conversion of infared images have become
  accessible due to the understanding of pitch in a
  liquid crystal.

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References

• 1.LIQUID CRYSTAL. The Columbia Encyclopedia,
  6th ed. New York Columbia University Press.
  ltwww.bartleby.comgt 2001-04.
• 2. Georgia Tech Investigates Liquid Crystal
  Polymer for NASA Applications. Georgia Institute
  of Technology. lthttp//www.physorg.comgt. 2006.
• 3. Gosta Ekspong. The Nobel Prize in Physics
  1991.World Scientific Publishing Co., Singapore,
  1997.
• 4. Liquid Crystal Phases. lthttp//plc.cwru.edu
  gt 2006.
• 5. Robert F. Service, Science. Vol. 292.
  5518, pp.825-826. 2001.
• 6. De Gennes, P.G., Prost, J. The Physics of
  Liquid Crystals. 2nd ed. Oxford University Press,
  New York. 1993.
• 7. A.M. Glazer. The Structures of Crystals.
  Adam Hilger, Bristol.1987.
• 8. Sparks, H. Bio-weapons Liquid Crystal
  Sensor. lt www.space.com gt. 2000.
• 9. Buka, A. Modern Topics in Liquid
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• 10. Johnston, B. A Gallery of Liquid Crystal
  Photomicrgraphs.
• ltwww.microscopy- uk.orggtMicscape Magazine.2003.
• 11.LiquidCrystal.Wikepedia.ltwww.wikipedia.com gt
  
• 12. Lavrentovich, O. About Liquid Crystals.
  lt www.lci.kent.edu gt.
• 13. Desimpel, C. The Basics About Liquid
  Crystals. lt www.elis.ugent.be gt.
• 14. Allen,M.TheoreticalPhysics.
  ltwww2.warwick.ac.ukgt.
• 15. Shakhashiri, B.Chemical of the Week. ltwww.
  scifun.chem.wisc.edugt.

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Thank You